BRPI0411338B1 - POLYMERIZATION PROCESS INVOLVING INITIATOR DOSAGE - Google Patents

Abstract

The invention relates to a polymerization process wherein at least one peroxide, with a half life in between 1 hour and 0.001 hour at the polymerization temperature at the moment of dosing, is dosed to the reaction mixture at the polymerization temperature and wherein at least during part of the period in which the peroxide is dosed i) the cooling means of the reactor are kept at essentially maximum cooling capacity and ii) the amount of initiator that is dosed is actively controlled such that the desired polymerization temperature is achieved and maintained within 0.3° C. of said polymerization temperature.

Description

Report of the Invention Patent for "POLYMERIZATION PROCESS INVOLVING INITIATOR DOSAGE". The present invention relates to a polymerization process wherein at least one peroxide, with a half-life between 1 hour and 0.001 hours at the polymerization temperature, is metered into the reaction mixture at the polymerization temperature and at least during part of the period during which the peroxide is metered i) the reactor cooling medium is maintained at essentially maximum cooling capacity and ii) the amount of primer that is metered is actively controlled.

Such a process is known, inter alia, from WO 03/54040. It is described herein that in a first step of a polymerization process part of the initiator having a half life of 0.001 hours to 0.050 hours at the polymerization temperature is initially dosed to achieve the desired maximum cooling capacity which is acceptable from the point of view. safety at the end of this dosage. In a second step the remaining primer is dosed to control the polymerization so that the maximum cooling capacity is maintained. The disadvantage of this process is that the temperature of the reaction mixture can fluctuate greatly around the desired polymerization temperature. Due to these temperature fluctuations, the reproducibility of the polymer obtained in terms of its K value between the different batches is undesirably low. This low reproducibility may lead to difficulties in processing the polymer produced, for example when the product is extruded, some physical properties of the extrudates will not meet the required specifications. Therefore, additional measures such as product analysis, separation of good and bad products may be necessary, making the process more costly. Moreover, the space-time yield of such a process is not optimal.

It is an object of the present invention to provide an improved polymerization process whereby polymers can be produced with greater reproducibility in terms of their K value.

This is achieved by using a polymerization wherein at least one peroxide, with a half-life between 1 hour and 0.001 hour at the polymerization temperature at the time of dosing, is dosed into the reaction mixture at the polymerization temperature and where at least for part of the period during which the peroxide is metered i) the reactor cooling medium is maintained at essentially maximum cooling capacity and ii) the amount of primer that is metered is actively controlled by a temperature controller so that the desired polymerization temperature is achieved and maintained within 0.3 ° C of said polymerization temperature.

Preferably, the polymerization temperature is maintained within 0.2 ° C of said polymerization temperature, more preferably within 0.1 ° C of said polymerization temperature.

By maintaining the polymerization temperature within the indicated temperature range while using the maximum reactor cooling capacity, the obtained polymer can be reliably and reproducibly produced in terms of its K value. Typically, the K value of the polymer is within 0.3 units of the predetermined K value, preferably 0.25 units of the predetermined K value, more preferably within 0.2 units of the predetermined K value.

By the term "essentially maximum cooling capacity" is meant that the controller (or controllers) used to regulate the temperature of the reaction mixture requires (requires) total cooling on average for at least 80% of the time, preferably by at least 85% of the time, more preferably at least 90% of the time, and even more preferably at least 95% of the time. In a more preferred embodiment, cooling is at its maximum capacity, which means that all available cooling capacity is used during the dosing period. Preferably, this is achieved by opening a valve either allowing the cooling medium to reach the polymerization reactor without being limited by other control means. It should be noted that the maximum capacity mentioned in this document is greater than the conventional capacity used in practice, which was, admittedly, also called the maximum capacity or total cooling capacity. More specifically, the conventional maximum capacity used in practice was the cooling capacity that was feasible for use in the process without breaching the safety margins, hence the conventional term termed maximum cooling capacity as used herein minus one. small capacity deemed necessary for safety reasons as explained below.

It should be noted that essentially maximum cooling capacity will only be required during part of the period in which the peroxide is being dosed. Typically, in another part of the polymerization process, especially at the beginning and near the end of the polymerization, for example, when monomer conversion is greater than 80%, for vinyl chloride polymerizations typically in the time period. As the pressure in the reactor drops, the essentially maximum cooling capacity will not be used.

In the context of the present application the term "the desired polymerization temperature is reached" means that the predetermined polymerization temperature is reached from the point where it can be maintained within 0.3 ° C of the desired temperature. Generally, the desired temperature is reached after heating of the reaction mixture and the initial temperature is exceeded. The size of the initial temperature rise is not essential. Generally, this increase is below 6 ° C of the desired polymerization temperature, preferably below 4 ° C, more preferably below 2 ° C, even more preferably below 1 ° C, and even more preferably below. at 0.3 ° C of the desired polymerization temperature. It is preferable that the temperature rise be the same or only slightly different for each batch so that reproducibly polymers having K values within the aforementioned variations around the predetermined K value are obtained. The range of initial temperature increases between batches is typically below 1 ° C, preferably below 0.5 ° C, more preferably below 0.3 ° C. The polymerization temperature is typically controlled by a temperature controller suitable for the reaction mixture temperature within the desired range of 0.3 ° C or less from the predetermined polymerization temperature. Preferably, the temperature controller is selected from the group consisting of a PID controller, a PI controller, a PD controller, and an undefined logic controller. These temperature controllers can use various algorithms such as PID, undefined logic, or model-based control algorithms.

These temperature controllers are capable of controlling the reaction mixture temperature by monitoring the reaction mixture temperature and / or the gas phase pressure in the polymerization reactor during the polymerization reaction, while at the same time adjusting the dosage rate of the reaction mixture. initiator to the reaction mixture. Based on the difference between the measured value and the desired value, the temperature controller sends signals to a dosage unit. The metering unit generally comprises a peroxide storage container containing the peroxide to be metered and a metering rate control device such as a metering pump and optionally a flow meter.

Generally, the temperature controller uses an algorithm comprising proportional, integral, and derivative functions. The skilled person knows these algorithms and functions. The input parameters for each algorithm function can be the same or different. The temperature of the reaction mixture is measured using a temperature sensing device such as a Pt-100 temperature sensor. The gas phase pressure in the reactor is measured using a pressure gauge device such as a conventional pressure transducer.

In polymerization processes where a gas phase such as vinyl chloride (co) polymerization (VCM) is present, it is preferable that the input parameter for the proportional and integral functions be the temperature of the reaction mixture, and The input parameter for the derivative function is the gas phase pressure.

In conventional polymerization processes the temperature of the polymerization mixture is typically controlled by means of a PID controller. Such PID controllers typically use temperature sensing devices and / or pressure gauges. In general, temperature sensing devices can measure temperature in the range of 0 to 100 ° C, and the pressure gauge device can detect pressures in the range of 0 to 20 bar. The PID controller conventionally generates a signal that controls the reactor cooling and / or heating device. The use of these PID controllers and temperature control devices will typically result in a precisely controlled temperature of the reaction mixture. However, in a polymerization system according to the invention, in which rapid peroxide is dosed, it was observed that conventional control systems led to unacceptable temperature variations of up to 2 ° C. Then, unexpectedly, it was discovered that a conventional PID controller could be used, since the gain is set from the conventional value of 3 to about 20 to a value greater than 40, preferably greater than 60, more preferably greater than 65. although it should be less than 150 and preferably less than 100. Very good results were obtained at values of about 80. In this sense it is observed that the proportional band of a PID controller is defined as 100/100. gain. Accordingly, the proportional band used in the PID controller is generally preferably 0.6%, preferably at least 1.0%, and at most 2.5%. preferably at most 1.5%, and more preferably at most 1.25% around the desired temperature.

Therefore, another embodiment of the invention is a process wherein a conventional PID controller is used whose proportional gain or band is set to a value within the limits set forth above. Note that it is possible to use temperature sensing devices and / or pressure gauge devices that can detect temperatures or pressures in a range other than that described above. In this case, the gain can be adjusted to have the proportional band similar to those identified above.

It is observed that in processes where vinyl chloride (VCM) is (co) polymerized, the pressure is initially proportional to the temperature of the reaction mixture. This is due to the fact that the pressure in the polymerization reactor is predominantly determined by the VCM vapor pressure in the polymerization mixture. Near the end of the polymerization reaction, the VCM is depleted. At some point there is no more liquid VCM phase present and the pressure in the reactor begins to fall below the pressure before that temperature. After and / or during the pressure drop VCM is still present in the gas phase, but typically increasingly being adsorbed in water and the polymer phase of the reaction mixture. Pressure is typically measured in the gas phase of the reactor contents, while temperature sensing devices are typically located below the liquid / gas surface of the suspended VCM polymerizations. The PID controller input is traditionally one or more reaction mixture temperature sensors. For preferred polymerization processes where at least vinyl chloride is polymerized, it has been found to be beneficial for the reactor content pressure to be used as an input parameter. According to a non-limiting theory, it takes considerable time until the peroxide that is dosed is well mixed with the total reactor content, which will result in a delay in temperature measurement. However, it has been found that a pressure transducer measures a variation in the overall polymerization temperature instantaneously and much faster than the temperature probe. Therefore, we use pressure as the input parameter for the proportional, integral and derivative functions of the algorithm used in the temperature controller during the polymerization reaction. Preferably, with the pressure drop in the polymerization reactor, the temperature sensing device will assume at least partial control, and from the pressure drop the temperature is used as an input parameter for at least one function and preference for all algorithm functions. After much experimental work, it has been found that the pressure is not always equal due to the inert gases present in the VCM, but it is still a valuable input parameter if it is used to feed the derivative D of the controller.

In this case the temperature controller may be based in part on temperature and pressure at the same time. The most preferred choice is where input P (proportional) and input I (integral) are from one or more temperature sensors and input D (derived) is from pressure. Because the pressure transducer reacts much faster than the temperature probe, the proposed control system results in significantly improved control of the temperature setting. The terms integral and derivative typically have the classical heats, for example 999 and 150 seconds.

It has been found that with the traditional pressure gauge device and the corresponding high gain factors connected to the PID controller derivative input signal and the conventional temperature sensing device connected to the proportional and integral input signals of the PID controller. PID controller, it was possible to maintain the settings not only during the time the peroxide was dosed, but also during the phase of the process where the pressure dropped without the need to use full conventional temperature control again. The temperature increase during the pressure drop phase is kept small due to the high gain factor.

In vinyl chloride polymerizations the use of the pressure sensor input during the process pressure drop phase is optional. Alternatively, the pressure sensor input is not used in this part of the process, but derived function is again linked to a temperature sensor. This will result in more economical peroxide consumption and absence of small temperature rise.

In a more preferred embodiment of the present invention, the output of the PID controller is used to control the dosage and / or dosage rate of the initiator. It has been found that such a system allows the maximum cooling capacity to be used while still maintaining the reaction temperature very close to the predetermined value. It has been found that it is possible to control the reaction temperature within 0.2 ° C, most often within 0.1 ° C of the predetermined temperature. If vinyl chloride is polymerized, it is optional to set or maximize primer dosing to a predetermined level during the process pressure drop phase rather than by the controller, and the controller is then used to control the pressure. temperature at a fixed value or according to a temperature profile in a conventional manner by adjusting the cooling capacity. In this case the peroxide consumption will be more economical but the process time will increase a little. If desired, the PID controller may be part of a split-range controller known in the art. For example, there may be a controller portion that governs cooling capacity and another portion that controls dosage and / or dosage rate.

In a preferred embodiment, all initiator metering equipment including tubing, probe equipment, dosing pump and metering unit, optionally including a refrigeration unit and optionally including a primer storage tank, and optionally also including a PID controller, is interconnected and constructed to form a unit that can be handled and moved independently of the conventional polymerization reactor assembly. This allows such a unit to be installed when required, for example if a reactor has to operate at full capacity, & remove the unit when a conventional process has sufficient polymer. Also, this allows multiple polymerization reactors to be exchanged by the present process independently of one another.

Preferably, the initiator dosage unit comprises: (a) a temperature controller having at least one temperature input for receiving signals from a temperature sensing device and / or at least one pressure input for receiving signals. a pressure gauge device, and an output for sending signals to a dosage unit; and (b) a dosage unit comprising an initiator storage container that is connected to a dosage rate control device. The metering rate control device is known to the person skilled in the art, and generally comprises a metering pump and optionally a flow meter such as a mass flow meter.

A specific advantage of the process of the invention is the fact that certain conventional safety measures can be eliminated.

More specifically, in a conventional process, the reactor is typically equipped with a device that permits the metering of a light or radical terminator to the reaction mixture, and / or devices that allow the reactor contents to be poured where polymerization reaction is occurring thermally (which means that the reaction value is higher than that which can be removed by cooling, causing the polymerization reaction to be self-accelerating). With the present assembly the peroxide dosage is used to control the heat being generated, even though the cooling is at the (essentially) maximum level. In the event that the reaction mixture reacts too quickly, the controller will dispense a smaller amount of the rapid initiator, causing less reaction heat, and a subsequent leakage is prevented.

Also, a conventional process is typically operated slightly below maximum cooling capacity, even for conventional processes where a peroxide was dosed, because the dosing was set and some extra cooling capacity was needed for small ones. accidental changes in polymerization rate and / or small variations in cooling water temperature (which is comparable to small changes in polymerization temperature if no countermeasures are taken). For example, an unexpected momentary increase in peroxide dosage rate, for whatever reason, would increase the reaction heat above normal and this would require a little extra cooling capacity to prevent overheating. In the present process, the cooling capacity is simply set to the essential maximum, and the peroxide is dosed so that the temperature is controlled. As all cooling capacity is now used, the total output of the polymerization reactor can be safely increased.

Another advantage of the present process is that, if necessary, the polymerization may be interrupted (stopping the initiator dosage). The polymerization process can be restarted later simply by restarting the initiator dosage. The ability to conduct polymerization in this start-stop mode will reduce the amount of polymer and / or monomer that is discharged and will also result in a significantly shorter reactor shutdown time should a polymerization process need to be stopped. for example in case of an emergency.

As it is a prerequisite of the present process that polymerization does not occur when initiator dosing is interrupted, the peroxide being dosed must decompose rapidly enough to prevent any buildup in the reaction mixture. In practice this means that all peroxide that is dosed must decompose fast enough. Suitable initiators for use in the present process include the products described in WO 00/17245 having a half-life between 1 hour and 0.05 hours at the polymerization temperature. Preferably, the half-life of the dosed initiator is less than 0.5 hour, more preferably less than 0.3 hour, and even more preferably less than 0.2 hour, always at the polymerization temperature. However, the products disclosed in WO 02/54040, with a half-life of 0.0001 hour to 0.05 hour at polymerization temperature, may also be used. More preferably, the half-life of the initiator dosed in the process of the present invention ranges from 0.01 to 0.2 hours at the polymerization temperature. Primer half-lives can be determined by conventional thermal decomposition studies in monochlorobenzene, well known in the art (see for example the "Initiators for high polymers" code 10737 which can be purchased from Akzo Nobel). Preferred examples of organic peroxides used in the process of the invention are 1,1,3,3-tetramethyl butylperoxy methoxy acetate, tert-butylperoxy methoxy acetate, tert-amylperoxy methoxy acetate, tert-butylperoxy ethoxy acetate, diisobutanoyl peroxide (Trigonox® 187), hexanoyl pivaloyl peroxide, 2-ethylbutanoyl-isononoyl peroxide, isobutanoyl-lauroyl peroxide, isobutanoyl-isononoyl peroxide, bis (tert-butylperoxy) oxalate, cyclododecyl-tert-butoxy-2,2-tertiary butoxy -bis-2-ethylhexanoylperoxy-4-methylpentane, 2,2-bis-2-ethylbutanoylperoxy-4-methylpentane-2,2-bis (2,2-dimethylpropanoyl peroxy) -4-methylpentane, 1- (2 -ethylhexanoylperoxy) -1,3-dimethylbutyl-1-peroxypivalate (Trigonox® 267) or 2,4,4-trimethylpentyl-2-peroxyneodecanoate (Trigonox® 423), tert-amyl peroxyneodecanoate (Trigonox®®) 123), tert-butyl peroxyneodecanoate (Trigonox® 23), benzene (m, p) di (2-isopropyl-2-peroxyneodecanoate), 2-methyl-4-hydroxypentane-2 peroxyneodecanoate, α-cumyl peroxyneodecanoate (Trigonox® 99) and peroxydicarbonates such as di-sec-butylperoxydicarbonate (Trigonox® SBP), di (4-tert-butylcyclohexyl) peroxydicarbonate (Perkadox® 16) and di (2-ethylhexyl) peroxydicarbonate (Trigonox® EHP).

Since it may be more efficient not to dose the entire primer, preferably based on the temperature controller output, but to dose part of the primer, which may be one or more primers and which may be the same or different from the primer that is dosed, to the reaction mixture at a given time, for example at the beginning of the polymerization process, the present process includes a process wherein one or more initiators are dosed without being dosed and / or which are dosed in a particular manner. - at any given time and in a certain amount. The present process can be used for various polymerization processes of various (co) monomers. However, it is preeminently suitable to polymerize mixtures of monomers comprising vinyl chloride monomer (VCM). Preferably, the process according to the invention involves the polymerization of monomer mixtures comprising at least 5 wt% (wt%) of VCM, preferably at least 10 wt%, more preferably at least 20 wt%. % w / w, and even more preferably at least 50% w / w, based on the weight of all monomers. The comonomers that may be used are of the conventional type and include vinylidene chloride, vinyl acetate, ethylene, propylene, acrylonitrile, styrene and (meth) acrylates. More preferably, at least 80% w / w of the monomers being polymerized are comprised of VCM, whereas in the most preferred process the monomer consists essentially of VCM. As is well known in the art, the polymerization temperature of these processes largely determines the molecular weight of the resulting resin. The process according to the invention relates to the polymerization of monomer mixtures comprising vinyl chloride monomer (VCM). Comonomers that may be used are of the conventional type and include vinylidene chloride, vinyl acetate, ethylene, propylene, acrylonitrile, styrene and (meth) acrylates. More preferably, at least 80% w / w of the monomers being polymerized are comprised of VCM, whereas in the most preferred process the monomer consists essentially of VCM.

As is well known in the art, the polymerization temperature of these processes largely determines the molecular weight of the resulting resin.

Also, the polymerization process may be conducted as a mass process wherein the reaction mixture is predominantly monomer or as a suspension process wherein the reaction mixture is typically a monomer suspension in water, or as an emulsion or microemulsion process wherein the monomer is typically emulsified in water. Preferably, the present process is a bulk, suspension or emulsion process. More preferably, it is a suspension polymerization process. In these processes it will be necessary to use the usual additives. For example, if the monomer is present as a suspension in water, the usual additives such as surfactants, protective colloids, antifouling agents, pH buffers etc. may be present. Depending on the type of polymer desired, each of the above mentioned processes may be preferred. It should be noted that conventional emulsion and suspension polymerization processes are completely different, not only in terms of the initiation system that is typically used, but also because the process conditions differ greatly.

It should be understood that the word "dosage" is used to describe the step of dosing the initiator to the polymerization reaction mixture under the polymerization conditions. Dosing may be done intermittently during polymerization, which means that at least two portions of Primer are dosed into the reaction mixture, or it may be continuous, which means that for a certain period of time the primer is conditional. - continuously dosed to the reaction mixture, or any combination of these techniques. Examples of a combination of these techniques include, for example, a process wherein the initiator is first continuously dosed, then dosing is stopped, and then it is continuously re-dosed. If an intermittent operation is chosen, there will be at least 2, preferably at least 4, more preferably at least 10, and most preferably at least 20 times when the initiator is metered at the polymerization temperature. More preferably, the peroxide is dosed continuously and / or intermittently from the beginning of the polymerization reaction, preferably after at least 5%, less preferably after at least 10%, even less preferably after at least 20% of the monomers already have been polymerized and wherein during the dosing period at least 2, preferably at least 5, more preferably at least 10%, even more preferably at least 20%, more preferably at least 40%, and even more preferably at least 40%. At least 60% of all monomer used in the process is polymerized. As has been said, it is more preferable to dose the initiator based on the signal from the temperature controller while cooling capacity is maintained at its maximum. The term polymerization temperature as used herein is used in its conventional connotation and represents the temperature that is desired to polymerize the monomer. As the temperature may vary accidentally or intentionally, it is generally assumed to be temperature during the period when most of the entire monomer (ie more than 50% w / w, preferably more than 60% w / w, more preferably more than 75% w / w of the monomer being polymerized) is being polymerized. It is known that the polymerization temperature setpoint may vary over time. Known polymerization temperature variations for vinyl chloride polymerizations include a higher intentional temperature when polymerization is initiated and / or a higher temperature with pressure drop, both of which are used to increase reactor output. If a variation of the polymerization temperature is applied, then the polymerization temperature is considered to be the average temperature over time. It is noted that also in the process of the present invention, the polymerization temperature setpoint during the starting and pressure drop stages may be higher than the average polymerization temperature setpoint. This can be a fixed value or a temperature profile. For the present process wherein the initiator is dosed, the polymerization temperature is the temperature at the time of dosing. The metered initiator may be a redox initiation system. In this case the reducing agent, oxidizing agent or both may be metered according to the invention. For such redox systems, the half-life of the redox system is the half-life measured when all system components are present. However, in view of the fact that redox systems typically contain heavy metals and / or unwanted reducing agents, the initiators of the present invention preferably are not such redox initiation systems. The dosed primer may be a single primer or a mixture of several primers. If a mixture is used, all initiators of said mixture must meet the half-life requirement. The initiator that is dosed to the reactor may be in pure form or preferably in the form of a dilute solution or dispersion (such as a suspension or emulsion). One or more suitable solvents may be used to dilute the initiator. Preferably such solvents are readily removed during the polymer treatment steps after the polymerization process (such as alcohols), or they are such that it is acceptable to leave them as a residue in the final polymer. Furthermore, it may be advantageous, but not necessarily obligatory, that such solvents do not negatively affect the thermal stability of the initiator dissolved in them, which can be verified by analyzing the half-life temperature of the initiator in said solvent. An example of a suitable solvent is isododecane. If an initiator dispersion is dosed, then the dispersion may be from the initiator itself or a solution of the initiator, preferably in suitable solvents. More preferably, the initiator to be metered in the present process is an aqueous dispersion. Preferably, the initiator is dosed at a concentration of 0.1 to 60% w / w, more preferably 0.5 to 40% w / w and most preferably 2 to 30% w / w. More dilute initiator solutions or dispersions ensure rapid mixing of the peroxide and polymerization mixture, leading to more efficient use of peroxide.

It may also be beneficial to dose the initiator together with a protective colloid. The total amount of initiator to be used in a process according to the invention varies within the range conventionally used in polymerization processes. Typically, 0.01 to 1% w / w of primer is used, more specifically 0.01 - 0.5% w / w, based on the weight of the monomers to be polymerized. The amount of metered initiator used is preferably at least 0.01 wt% (% w / w), more preferably at least 0.015 wt%, and most preferably at least 0.02 wt%, always based on the weight of the monomer that is polymerized in the process.

Preferably, the initiator dosage may be carried out at any suitable entry point for the reactor. If water is dosed in the course of the polymerization process, for example to compensate for the reduction in reactor content due to the polymerization reaction, it may be advantageous to use the conduit through which this water is dosed to also dose the polymerization reaction. initiator. If a feed line is used to dose the initiator, it may be dosed below or above the surface of the liquid in the reactor. If the reactor is equipped with a condenser, the peroxide can be metered through the condenser. It is noted that if the formation of the initiator is sufficiently rapid, it is possible to introduce the raw materials for said initiator into pumping containers or to wait for where the initiator is then introduced into the polymerization mixture. Alternative, but no less desirable, is the process in which the raw materials are metered into the polymerization mixture. In all cases it may be beneficial to add stirring equipment and / or heat exchangers to the feed ducts to optimize efficiency.

After polymerization, the resulting (co) polymer (or resin) will be treated as usual in the art. Polymers obtained by suspension polymerization according to the invention, for example, will be subjected to the usual drying and sieving steps. The resulting resin preferably comprises less than 50 ppm primer, more preferably less than 40 ppm, even more preferably less than 25 ppm primer, immediately after drying for 1 hour at 60 ° C. and sifting. The resin has been found to exhibit excellent thermal stability measured with a Metrastat® PSD260 test furnace using ISO 182-2 (1990E). Improved thermal stability has proven that the resin is unlikely to fade when subjected to melt processing steps, for example to form molded articles. The process of the invention is illustrated in the following examples.

Examples Example 1 and Comparative Example A

A conventional vinyl chloride polymerization process * in which the cooling rate was controlled and the peroxide dosed at the beginning of the polymerization was compared to a process in which during part of the polymerization the cooling rate was set at maximum capacity and a controller. PID was used to control primer dosage rate.

A significant increase in polymerization rate was observed, allowing for shorter reactor times.

Experiments were performed according to a standard suspension polymerization process using a 10 I Büchi reactor equipped with a baffle plate, three three-level flat paddle stirrers, a pressure transducer (having a pressure response of 1, 67 mV / bar), a temperature sensing device includes a Pt-100 sensor, a vinyl chloride feed line (VCM), a nitrogen purge line, a peroxide metering line, and a peroxide. The reactor is charged with 4,700 g of demineralized water, 40.2 g of a 5% solution of Alcotex® B72 (polyvinyl acetate / alcohol) in demineralized water, and pressurized with nitrogen to 15 bar. If no leakage is observed, the reactor is evacuated for 5 min at 75 mbara (with agitation) to remove air, and subsequently loaded with 2,870 g of VCM (ex Shin Etsu Pernis), followed by heating of the reactor to r. desired polymerization temperature of 57 ° C in 30 - 60 minutes.

Temperature sensing devices have been connected to all input sin3 * s of the PID controller used to control temperature.

After reaching a stable temperature, the initial peroxide is dosed through the injection point in 1 minute (conventional - comparative example) or dosed over time to the reaction mixture (example 1). In the comparative example, the PID controller has regulated the flow of the heating / cooling device. In Example 1, until the point at which dosing began and the moment of pressure drop, the temperature was conventionally controlled with the PID controller regulating the flow of the heating / cooling device. During the dosing period, It used essentially maximum cooling capacity and the output of the PID controller was used to control the dosing rate of the initiator.

In the conventional process, the maximum polymerization rate (33% / h) was obtained immediately before the pressure drop phase. The essentially maximum cooling capacity was equal to the cooling capacity that was required at this polymerization rate.

Accordingly, during part of the process according to the invention the (very) rapid peroxide dosing through the feed duct was made such that the temperature of the reaction mixture was maintained at 57 ° C in that cooling capacity. Said cooling capacity and dosage began 0.5 - 0.65 hours after the reaction medium reached a temperature of 57 ° C. The polymerization was interrupted when a pressure drop of 2 bar was reached, cooling the reactor and degassing it. After removal of residual VCM by evacuation, the polymer was obtained by filtration, washing and drying. When an aqueous dispersion of the initiator is added during the process, the expected dosed volume is subtracted from the amount of water dosed at the beginning, so that the total amount of water will be (more or less) the same at the end of the reaction.

Using the experimental setup described, a conventional primer (Trigonox® EHP ex Akzo Nobel) was used as initiator. In Comparative Example This primer was used as the sole primer and it was found that 656 ppm was the maximum amount that could be used with the reaction mixture maintaining the desired reaction temperature of 57 ° C, even at absolute maximum cooling.

In Example 1, the initiator, Trigonox® 187 (a diisobutyryl peroxide ex Akzo Nobel formulation) was dosed continuously during the polymerization process as a dilute aqueous dispersion. The parameters used for the conventional process and for the continuous primer dosing process are given in Table 1. The time to pressure drop (CPT) as well as the time until pressure has dropped to two bar below the pressure at the beginning of the pressure drop, are also reported as a measure of the polymerization rate.The amount of polymer obtained is presented as the monomer yield (yield) .The table also shows the average particle size of the polymer "(psd).

From the results it follows that much shorter process times can be obtained with continuous initiator dosing than with conventional processes.

Example 2 and Comparative Example B

In Example 2 and Comparative Example B the experimental setup of Example 1 was used. The primer used in both examples was Trigonox® 187. The parameters of the PID controller used during the eXPer 's are shown in the Table below.

In example 2 the temperature of the reaction mixture is kept within 0.2 ° C of the predetermined polymerization temperature of 57 ° C.

In comparative example B, the reaction mixture is kept within 2 ° C of the predetermined temperature, and only 90 minutes after reaching the polymerization temperature after startup, the temperature is controlled within 0.3 ° C of the predetermined temperature. . From Table 2 it can be inferred that the time to pressure drop (CPT) as well as the time until pressure has fallen to a value two bar below the pressure at the beginning of the pressure drop are shorter for the pressure drop. In addition, the value K of the product of comparative example B is greater than the desired K value of 67.0, this desired value being obtained for the product of example 2.

Claims (7)

1. Polymerization process in which vinyl chloride is polymerized, optionally together with other monomers, where at least one peroxide, with a half-life between 1 hour and 0.001 hours at the polymerization temperature at the time of dosing, is dosed into the mixture. reactive at polymerization temperature wherein at least for part of the period in which the peroxide is metered i) the reactor cooling medium is maintained at essentially maximum cooling capacity such that one or more controllers are used to regulate the temperature of the reaction mixture to order complete cooling on average at least 80% of the time and (ii) the amount of initiator that is dosed is actively controlled by a temperature controller so that the desired polymerization temperature is reached and maintained within 0.3 ° C of said polymerization temperature. Polymerization process according to claim 1, characterized in that the polymerization temperature is maintained within 0.2 ° C, preferably within 0.1 ° C, of said polymerization temperature. Polymerization process according to one of Claims 1 and 2, characterized in that the temperature controller controls the temperature of the reaction mixture by monitoring the temperature of the reaction mixture and / or the gas phase pressure in the polymerization reactor during the reaction. polymerization while at the same time adjusting the dosage rate of the initiator to the reaction mixture. Polymerization process according to any one of claims 1 to 3, characterized in that the temperature is controlled by a temperature controller selected from the group consisting of a PID controller, a PI controller, a PD controller, and a controller. logical undefined. Polymerization process according to claim 4, characterized in that the controller is a PID controller using a proportional band, characterized in that the proportional band of the PID controller is in the range of 0.6% to 2.5%. Polymerization process according to claim 5, characterized in that the temperature sensing device is connected to the proportional and integral input signals of the PID controller and where the reactor pressure sensing device is connected to the function derived from the PID controller during at least part of the period in which the peroxide is dosed. Polymerization process according to any one of claims 1 to 6, characterized in that the polymerization process is a suspension polymerization process.